Links on form design

Website Form Usability: Top 10 Recommendations by Kathryn Whitenton, Nielsen Norman Group
Design Better Forms — Common mistakes designers make and how to fix them by Andrew Coyle
Sensible Forms: A Form Usability Checklist by Brian Crescimanno, A List Apart
Better Form Design: One Thing Per Page (Case Study) by Adam Silver
20 Guidelines for Usable Web Form Design, J.A. Bargas-Avila, O. Brenzikofer, S.P. Roth, A.N. Tuch, S. Orsini and K. Opwis, University of Basel
Avoid Multi-Column Forms by Jamie Appleseed, Baymard Institute
Placeholders in Form Fields Are Harmful by Katie Sherwin, Nielsen Norman Group